Plastics like the fibers in t-shirts and the abrasive beads in body wash are polluting rivers more than previously thought, according to researchers from the University of Montana’s Flathead Lake Biological Station.

Rivers carry up to four million tons of plastic each year. Until recently, the common knowledge was that most, if not all, of that plastic pollution was flushed to the ocean.

But Chinese researcher Xiong Xiong says microscopic plastic debris is polluting rivers more than previously thought, especially around large cities and even in sediments in the river bottom. He says his findings could help managers locate and address the source of the pollution to protect human and ecosystem health.